Tire having crown reinforcement

ABSTRACT

A radial &#34;heavy vehicle&#34; tire, of H/S form ratio of at most 0.60, with a  wn reinforcement (2) composed of at least two crossed working plies (21, 22), and at least one ply (20) of circumferential cables arranged above the carcass ply (1) and a tread (10) of width L, characterized in that there is arranged, between the ply of circumferential cables (20) and the first, radially innermost, working ply (21), a layer of rubber mix (4) of low modulus of extension, of constant thickness of between 2 and 3 mm. and having a width LM equal to L21, while the second, radially outermost, working ply (22), of axial width L22, which is greater than the width L21, is separated radially from the edge of the ply of circumferential cables (20), firstly by a rubber cushion (5) of a high modulus of extension, extending axially from the end of the working ply (21) beyond the end of the ply of circumferential cables (20), and secondly, radially on the outside of said cushion (5), by a wedge of rubber (6) of a modulus which is intermediate the low modulus and the high modulus and extends axially substantially from the edge of the radially outer working ply (22) to a point axially on the inside of the end of the working ply (21).

BACKGROUND OF THE INVENTION

The present invention relates to a tire with radial carcassreinforcement of low H/S form ratio, which tire is particularly intendedto be fitted on a heavy road vehicle.

Such a so-called "heavy vehicle" tire comprises a radial carcassreinforcement, generally formed by a single ply of radial metal cablespreferably made of steel, said ply being anchored in each bead to atleast one bead wire, which itself is made of metal, having a compositionand a shape matched to the inclination of the bead seat, in order toform an upturn. The skeleton of the tire is completed by a crownreinforcement which hoops the carcass reinforcement. Said crownreinforcement is generally composed, radially from the carcassreinforcement to the outside, of a ply or two half-plies calledtriangulation plies, two plies called working crown plies and one or twoplies called protective plies. The triangulation halfply or plies, theobject of which is to prevent the subjacent cables of the carcassreinforcement becoming compressed, are formed of inextensible metalcables, forming a large angle, possibly being between 50° and 90°, withthe circumferential direction. The working crown plies are formed ofinextensible metal cables, crossed from one ply to the next, formingwith the circumferential direction angles, which may be equal or notequal, which are generally small, of between 15° and 35°. As for theprotective plies, they are formed of elastic cables which form with thecircumferential direction angles o f a value similar to that of theangles of the cables of the working plies.

Such a crown reinforcement structure is very widely used in the "heavyvehicle" tires of H/S form ratio ≧0.8, and is completely satisfactory.On the other hand, for many reasons it is difficult to apply to tires ofH/S form ratio <0.60.

In order to solve one of the problems set, namely controlling themeridian profile of the tread, it has been proposed, for example inFrench Patent 2 566 334, to replace the triangulation ply (plies) with aply of inextensible circumferential or quasi-circumferential cables, theaxial ends of which are axially on the outside of the ends of the twoplies of crossed cables, which complete the crown reinforcement of thetire described in the afore-mentioned patent.

For the same reasons as previously, French Patent 2 419 185 recommendsthe use of two hooping reinforcements located on either side of theequatorial plane, each reinforcement being composed of two plies of lowwidth and of inextensible metal cables crossed from one ply to theother, forming a preferably small angle of 5° to 0° with thecircumferential direction.

Although such crown reinforcement structures have the advantage ofgreatly reducing the risk of separation between the ends of the workingplies, at the same time as they make it possible to avoid the formationupon inflation of the concave shape of the tread, on the other hand theyare not sufficiently effective for overcoming a specific problem of thedimensions of the tire in question, namely the risks of the cables ofthe carcass ply becoming compressed, a ply of circumferential cables notbeing at all effective in solving such a problem.

It is possible to overcome the above disadvantages by various means, forexample by redimensioning the cables of the carcass ply so as to makethem more resistant to fatigue by compression. Another means consists incontrolling the transverse contraction of the crown reinforcement. Thecurrent known means, generally consisting in increasing the metallicmass of the reinforcements, result in an increase in the cost of thetire.

SUMMARY OF THE INVENTION

In order to overcome the above disadvantages, the tire of H/S form ratioof <0.60, according to the invention, and principally comprising acarcass reinforcement composed of at least one ply of radial cables, acrown reinforcement composed of at least two so-called working plies ofinextensible metal cables crossed from one ply to the next, formingangles of between 15° and 35° with the circumferential direction, and atleast one ply of circumferential cables arranged between the outermostply of radial cables and the first, radially innermost, working crownply, said ply of circumferential cables having ends axially beyond theends of the working plies and said crown reinforcement being surmountedby a tread of width L, characterized in that there is arranged betweenthe ply of circumferential cables, of a width L20 of between 0.8 and0.95 L, and the first, radially innermost, working ply, of a width L21of between 0.5 and 0.7 L, a layer of rubber mix of low modulus ofextension, of constant thickness of between 2 and 3 mm and having awidth LM equal to L21, whilst the second, radially outermost, workingply, of axial width L22, which is greater than the width L21, isseparated radially from the edge of the ply of circumferential cables,firstly by a rubber cushion of a high modulus of extension, extendingaxially from the end of the first working ply beyond the end of the plyof circumferential cables, of a thickness practically equal to the totalthickness of the first working ply and of the layer of rubber of lowmodulus, and secondly, radially on the outside of said cushion, by awedge of rubber of a modulus which is intermediate between the lowmodulus and the high modulus and extends axially substantially from theedge of the second working ply to a point axially on the inside of theend of the first working ply by a quantity of between 0.03 and 0.10times the width L21, said wedge permitting the uncoupling of the edgesof the working plies.

"Rubber mix, obviously vulcanized, of low modulus of extension" is to beunderstood to mean a mix, the secant modulus of which at 10% relativeelongation is between 3.3 and 3.7 MPa. A mixture of a high modulus ofextension will have a modulus, measured under the same conditions, ofbetween 10 and 20 MPa, whereas a mix of a modulus intermediate betweenthe two preceding ones will have a modulus, of the same name andmeasured under the same conditions, of between 6 and 9 MPa.

The combination of the widths, respectively of the ply ofcircumferential cables and of the working crown plies, with thearrangement optimized in quality and location of the layers of rubberbetween the different plies mentioned makes it possible not only toavoid the risks of the cables of the normally designed carcass plybecoming compressed, but also to improve the resistance to separationbetween the edges of the working plies, owing to the blocking undertransverse stress of the complex formed by the ply of circumferentialcables, the layer of rubber radially on top and the first working ply,whereas the edges of said working plies are separated by rubber having aconventional modulus of extension, contrary to a certain teaching (seeFrench Patent 1 290 231) recommending the separation of such edges by awedge of rubber of great hardness.

The separation between working plies may, within the scope of theinvention, be improved firstly by the presence, radially above thesecond, radially outermost, working ply, of a ply of elastic cablesoriented in the same direction as that of the cables of the subjacentsecond working ply, but of axial width L23 greater than L22 and lessthan L20. Said protective ply is then advantageously separated from thecomplex described above by a wedge of rubber mix of low modulus ofextension, identical to the modulus of the rubber layer located betweenthe ply of circumferential cables and the first working ply.

DESCRIPTION OF THE DRAWING

The characteristics and advantages of the present invention will bebetter understood with reference to the following description, whichrefers to the drawing illustrating an example of embodiment innon-limitative manner, in which drawing:

FIG. 1 is a diagram of a meridian section through the upper part of atire according to the invention,

FIG. 2 is an enlargement of the circled part of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

The tire according to the invention, of dimension 495/45-22.5 has an H/Sshape ratio substantially equal to 0.45, H being the height of the tireupon rim and S being the maximum axial width of said tire mounted on itsoperating rim 22.5×17.00 and inflated to a recommended pressure of 9bar.

Said tire mainly comprises a carcass reinforcement formed, in the casedescribed, of a single ply 1 of metal cables made of steel, capable ofresisting a tensile force which is very clearly greater than the tensileforce generated by the inflation pressure of the tire. This carcassreinforcement 1, isolated from the inflation gas by the inner layers ofrubber, as is known per se, is surmounted radially on the outside by acrown reinforcement 2. Said crown reinforcement 2 is formed, passingradially from the inside to the outside, by a ply 20 called hoopingcrown ply, formed of metal cables made of steel, the modulus of whichmakes it possible to impart to said ply 20 a stiffness in extension perunit of width of between 3300 and 9000 daN/mm (the stiffness inextension is the ratio of the extension force applied to the unit ofwidth of the ply in order to obtain a given elongation in the directionof the circumferential cables). The ply 20 has a width L20 of 380 mm,namely 0.90 times the width L of the tread 10 of the tire. It isseparated radially on the outside from the first working ply 21 by alayer of rubber mix 4. The ply 21 is formed of inextensible metal cablesmade of steel, which enables it to have a stiffness in extension perunit of width, perpendicular to the direction of the cables, of between5500 and 8000 daN/mm, and forming an angle of 18° D with thecircumferential direction. The ply 21 has a width L21 of 260 mm, namely0.6 times the width L of the tread 10. The layer of rubber mix 4 has awidth LM which is exactly equal to the width L21, has a thickness ewhich is constant over said width and equal to 2.5 mm and has a modulusof extension at 10% relative elongation of 3.5 MPa.

Axially on the outside of the ends of the first working ply 21 and ofthe layer 4, there is arranged on the ply 20 of circumferential cables acushion 5 of rubber mix which may have a constant thickness or onedecreasing with increasing distance from the above ends, and a widthsuch that said cushion covers the end of the ply 20. Said cushion 5 hasa high modulus of extension, equal to 12 MPa.

The first working crown ply 21 is surmounted radially on the outside bya second working ply 22, formed by the same metal cables made of steelas those of the working ply 21, and consequently having the samestiffness in extension per unit of width, said cables forming an angleof 18° G with the circumferential direction. The width L22 of thesecond, radially outermost, working ply 22 is greater than the width L21of 50 mm. which is why there is an axial distance of 25 mm between eachend of the first ply 21 and each end of the second ply 22.

Between the first working ply 21 and the second working ply 22 there isa triangular wedge of rubber mix 6 arranged such that it is insertedbetween the edges of said working plies over an axial width 1corresponding to 6% of the width L21 of the first, shortest, working ply21 and such that it covers the cushion 5 of rubber of high modulus overthe axial distance between the ends of the first working ply 21 and thesecond working ply 22 respectively. Said rubber wedge 6 has a modulus ofextension of 7.5 MPa.

The so-called protective ply 23 completes the crown reinforcement.Composed of so-called elastic metal cables, that is to say ones having arelative elongation of at least 2% under a force equal to 10% of thebreaking load, forming with the circumferential direction an angle equalto the angle formed by the cables of the second working ply 22, the ply23 has a width of 335 mm, that is to say greater than L22 but less thanL20. It is separated from the rubber cushion 5 by a second wedge 7 ofrubber mix having a modulus of extension equal to the modulus of thelayer 4 separating the ply 20 of circumferential cables from the first,radially innermost, working ply 21. In order to reduce the heating-up ofthe tire as much as possible, the crown reinforcement 2 is covered overwith a layer 8 of rubber mix of low hysteresis, that is to say, ahysteresis equal to half the hysteresis of the tread. Said layer 8 isitself surmounted radially by the tread 10.

I claim:
 1. A tire comprising a carcass reinforcement composed of atleast one ply (1) of radial cables, a crown reinforcement (2) composedof at least two working plies (21, 22) of crossed inextensible metalcables, the at least two working plies (21, 22) including a first,radially innermost, working ply (21) and a second, radially outermost,working ply (22), and at least one ply (20) of circumferential cablesarranged between the carcass reinforcement and the first, radiallyinnermost, working ply (21), said at least one ply of circumferentialcables (20) having ends axially beyond the ends of the working plies(21, 22) and said crown reinforcement (2) being surmounted by a tread(10) of width L, characterized in that there is arranged between the atleast one ply of circumferential cables (20), which has a width L20 ofbetween 0.8 and 0.95 L, and the first, radially innermost, working ply(21), which has a width L21 of between 0.5 and 0.7 L, a layer of rubbermix (4) of low modulus of extension, the layer of rubber mix (4) of lowmodulus extension having constant thickness of between 2 and 3 mm andhaving a width LM equal to the width L21, the second, radiallyoutermost, working ply (22), which has an axial width L22 which isgreater than the width L21, is separated radially from an edge of the atleast one ply of circumferential cables (20), firstly by a rubbercushion (5) of a high modulus of extension, extending axially from theend of the first working ply (21) beyond the end of the at least one plyof circumferential cables (20) and having a thickness practically equalto the total thickness of the first working ply (21) and of the layer ofrubber mix (4) of low modulus of extension, and secondly, radially onthe outside of said cushion (5), by a wedge of rubber (6) of a moduluswhich is intermediate between the low modulus and the high modulus, thewedge of rubber (6) extending axially substantially from an edge of thesecond working ply (22) to a point axially on the inside of the end ofthe first working ply (21) by a quantity of between 0.03 and 0.10 timesthe width L21, said wedge of rubber (6) permitting uncoupling of theedges of the working plies (21) and (22) wherein the tire has a heightto maximum axial width (H/S) ratio of <0.60.
 2. A tire according toclaim 1, characterized in that the crown reinforcement (2) is completedby the presence, radially above the second, radially outermost, workingply (22), of a protective ply (23) of elastic cables oriented in thesame direction as that of the cables of the subjacent second working ply(22), the protective ply (23) having an axial width L23 greater than thewidth L22 and less than the width L20, said protective ply (23) beingseparated from the cushion (5) by a wedge of rubber mix (7) of lowmodulus of extension, identical to the modulus of the layer of rubbermix (4) located between the at least one ply of circumferential cables(20) and the first, radially innermost, working ply (21).